A cost efficient solution for improving the performance and in particular the spatial coverage of Long Term Evolution (LTE) and LTE-Advanced (LTE-A) telecommunication networks is the utilization of relay nodes (RN), which allows installations without having terrestrial broadband access or the need to install micro wave links. In a relay enhanced telecommunication network there are basically three different types of radio connections:    A) A first type of radio connection is the connection between a base station (BS) and a user equipment (UE). This type of connection is called a direct link.    (B) A second type of radio connection is the connection between a BS and a RN. This type of connection is called a backhaul link or a relay link.    (C) A third type of radio connection is the connection between a RN and a UE. This type of connection is called an access link.
RNs are to become an intrinsic feature in particular for the LTE-Advanced technology and are currently undergoing a standardization process within 3GPP.
In a relay enhanced telecommunication network RNs have to serve two purposes: Firstly, they have to receive the radio transmissions from its serving BS, which is often also called donor BS. Secondly, they have to provide cellular coverage to UEs, which are located in those areas where the donor BS cannot provide sufficient service level. Those areas are for instance mobile service coverage holes such as indoor areas, which are due to building structures electromagnetically shielded from the donor BS. In order to achieve a high performance of a relay enhanced telecommunication network, the antenna characteristic, which is the spatial characteristic antenna pattern defining the radiation pattern of an antenna, has to be adapted to both above-described purposes. This means that one has to find a compromise between fulfilling these two purposes.
Typically, the first purpose, i.e. a good radio connection between the RN and the BS, is considered as to be much more important than the second purpose, i.e. good radio connection between the RN and US(s), because the backhaul/relay link has to carry data transmissions which are related to all UEs, which are currently connected to the RN. Further, the link between RN and BS will be used for backhaul traffic in the event of handover of a UE.
Specifically, an efficient improvement of indoor coverage requires that the radio link extending between the RN and its donor BS has a good or a very good quality, because this link will be used as backhaul for the RN, possibly to transfer huge amount of data both in the uplink (UL) and in the downlink (DL) direction.
If one considers cheap so called “all-in-one” box RNs, which have to be installed indoor, the need of providing a good quality for the radio link extending between the RN and its donor BS will cause that the RN has to be installed in the direct proximity of a window of the respective building. However, this may not be optimal from the indoor coverage point of view.
Generally speaking, known RNs do not ensure that the links to UEs can also have a high quality and this impacts the overall performance of the telecommunication network. A low quality link between a UE and a RN can lead to increase the retransmission of data or to a possible request for handover, both of which will consume radio resources and increase the amount of signaling. As a consequence, the performance of the telecommunication network decreases.
There may be a need for improving the performance of a relay enhanced telecommunication network.